1. Field of the Invention
The present invention relates to a data modulating system for recording information in an optical disk, etc.
2. Description of the Related Art
In general, a so-called 4/11 modulating system is often used when information is recorded to an optical disk, etc.
In this 4/11 modulating system, input data are are in an 8-bit code and are converted to an output code composed of 11 channel bits. In this conversion, 4 channel bits in the output code are set to a code "1" at any time with respect to the respective input data composed of 256 words. In general, when such a data modulating system in which the predetermined number of code "1" is assigned in the predetermined length of output code is used, a DC component in a reproduced signal is constant. Accordingly, it is easy to remove the change in DC voltage level of a transmission system by a method using AC coupling, etc. during a data reproducing process.
When the above mentioned data modulating system is used, it is possible to use a differential deflection system during a data reproducing process. A differential detection system determines the channel bit position having code "1" by comparing the reproduced signal level at every channel bit position and selecting the predetermined number of channel bit positions out of channel bits positions having a high level. Since a differential detection system reduces the influence of noise in the reproduced signal, the above modulating system is often used in an optical disk drive.
However, in the above-mentioned 4/11 modulating system, a large amount of memory capacity for a conversion table such as 256 words.times.11 bits is required so that it is difficult to reduce the cost of the data modulating system. Further, the amount of input data bits per one channel bit is equal to 8 bits/11 bits=0.7272 - - - and is therefore small so that conversion efficiency is low and it is impossible to increase recording capacity of the disk.